Air intake flowmeter for internal combustion engines

ABSTRACT

A volumetric air flowmeter for internal combustion engines, which includes a cast metal housing, a rectangular airflow channel therewithin, and a transversely-extending, trapezoidal-shaped pivotal baffle plate mounted on a pivot shaft. There is also provided on the pivot shaft a damping flap, angularly offset with respect to the baffle plate, which revolves, in unison with baffle plate deflection, about the shaft axis into a damping chamber. Circumferential clearances are provided between the baffle plate and its channel and between the damping flap and its chamber.

BACKGROUND OF THE INVENTION

The invention relates to a flowmeter having a cast metal housing, arectangular airflow channel therewithin, and a transversely-extending,trapezoidal pivotal baffle plate particularly for measurement of the airdrawn in by an internal combustion engine through the air intake duct.

Flowmeters of this kind are already known, for example, they are used infuel injection systems to ascertain the volume of air drawn intointernal combustion engines. In a typical application, thetransversely-extending pivotal baffle plate is deflected by athrottle-induced increase in the air flow until substantially the entirerectangular cross section of the flow channel is unrestricted. Inaddition, a spring mounted on the pivot shaft serves as an opposingforce to the air pressure exerted on the baffle plate, so that theangular deflection of the baffle plate is a measure of the volume of airflow through the channel. The housings of these known flowmeters are,e.g., zinc castings. A circumferential clearance is provided between thebaffle plate edges and the flow channel wall, amounting to approximately0.1 to 0.2 mm total. Though a narrow circumferential edge clearance is,for functional reasons, normally provided, a concomitant problem mayresult due to unrelieved internal stresses in the cast metal housings sothat in applications over a broad operating temperature range of theengine, e.g., from -40° C. to +120° C., the castings may expand unevenlyand the damping flap or baffle plate may make contact with the walls ofthe flow channel or damping chamber, thus impeding their free pivotalmotion.

OBJECT AND SUMMARY OF THE INVENTION

The object of this invention is to provide a baffle plate of known typewhich can be employed over broad temperature ranges, without incurringthe above-described problems.

This object is achieved, according to one embodiment of the invention,by positioning a trapezoidal-shaped baffle plate transversely of theflow channel, the longer of the parallel sides being mounted adjacentthe pivot shaft and the shorter, opposed, parallel side lying adjacentthe top of the flow channel.

According to an especially advantageous embodiment of the invention, thebaffle plate mechanism is provided with a damping flap, also mounted onthe pivot shaft, angularly offset with respect to the baffle plate andmoving in a rectangular-shaped damping chamber. The damping flap alsohas a trapezoidal-shaped cross section, and the damping flap edgeadjacent the pivot shaft is longer than the oppositely-disposed paralleledge.

The trapezoidal-shaped design of the baffle plate and the damping flapavoids contact with the walls of the flow channel and damping chamber,resulting from temperature-dependent expansion in the structuralelements thereof, yet the resultant clearance between the edges of theplate or flap and the walls of the flow channel remain within acceptablelimits.

BRIEF DESCRIPTION OF THE DRAWING

An exemplary embodiment of the object of the invention is shown in thedrawings and more fully described hereinafter.

FIG. 1 shows a cross section of the flowmeter;

FIG. 2 shows a cross section of the flowmeter along line II--II of FIG.1; and

FIG. 3 shows a detailed partial view of FIG. 2 on a larger scale.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIG. 1, the intake air of the internal combustion engineis drawn through a flow channel 2 in a housing 1, provided with a baffleplate 3 positioned in an air intake pipe (not shown) to individualcylinders of the internal combustion engine. The baffle plate 3 is heldin a bearing compartment 4 of the cast zinc housing 1 by a pivot shaft 5and ball bearings 6, 7 in a unilateral manner.

In the special application of the flowmeter in the air intake pipe of aninternal combustion engine, a safety valve 8 is disposed on the baffleplate 3 for the reduction of pressure shocks exerted opposite to the airflow directed against the baffle plate 3. For the damping of pulsations,a damping flap 9 is provided on the pivot shaft in spaced angularrelation thereto; the damping flap revolves on the axis of the pivotshaft 5 and moves in a damping chamber 10 when the baffle plate isdeflected by the air flow. The baffle plate is deflected against theforce of a spiral spring mounted on the pivot shaft (not shown). Theangular position of the baffle plate 3 or of the pivot shaft 5 may, forexample, be electrically measured using a potentiometer, as anindication of the air flow rate.

According to one embodiment of the invention, the baffle plate 3, andthe damping flap 9 are trapezoidal-shaped and so disposed that thelonger edge of the baffle plate 11 and that of the damping flap 12 lieadjacent the pivot shaft 5. In addition, FIG. 3 shows that the baffleplate 3 is provided with lateral clearances separating it from thechamber wall by the distance (a) at its longer edge and the distance (b)at its shorter edge, respectively, 0.12 mm and 0.25 mm. This embodimentof the invention prevents the adverse effects of temperature changesreferred to previously, i.e., rubbing contact of the plate or flap withthe walls as a result of uneven thermal expansion due to remanentinternal stresses in the casting, thus maintaining the required accuracyof the flowmeter.

The foregoing relates to a preferred exemplary embodiment of theinvention within the spirit and scope of which other embodiments andvariants are possible, the scope being defined by the appended claims.

What is claimed is:
 1. In a flowmeter for measuring the air intake flowin an internal combustion engine, including a cast housing, arectangular flow channel provided therein and a transversely extendingbaffle plate mounted on a pivotal shaft, the improvement comprising thatthe baffle plate is substantially trapezoidal-shaped having longer andshorter oppositely disposed parallel edge portions, the longer of saidedge portions lying adjacent said pivotal shaft.
 2. A flowmeteraccording to claim 1, wherein a trapezoidal-shaped damping flap isprovided on the pivotal shaft in spaced angular relation to said baffleplate and mounted to move within a rectangular walled, semi-circulardamping chamber, the damping flap further having longer and shorteroppositely-disposed parallel edge portions, the longer of said edgeportions lying adjacent said pivotal shaft.